One of the objectives of the proposed work is to study the effects of noise on the inner ear epithelium. Emphasis will be placed on the elucidation of the mechanisms which lead to damage of the cells and nerve fibers and how these injuries result in cellular death and, in some instances, degeneration of an entire segment of the organ of Corti or stria vascularis. Once a precise description of the initial effects of excessive exposure to noise is obtained, some of the theories of noise damage will be tested. Normal ears will be exposed to conditions with known mechanisms of action (i.e., metabolic inhibitors, various forms of hypoxia) and the changes which occur in these ears compared to those in the noise-damaged specimens. Another objective is to define the anatomical correlates of ischemia and other forms of hypoxia in the inner ear structures and to define the morphological changes which signify irreversible damage after repeated episodes of complete or partial anoxia. Evaluation of the damaged specimens will include detailed study of the embedded flat preparations by phase contrast microscopy so that counts of damaged or missing sensory cells can be made and percentages of these cells calculated. This examination will be followed by sectioning of selected areas of pathologic interest for light or electron microscopic study.